Precast panels, typically being finished on one side, offer numerous advantages in construction. In the majority of cases the cost of the building will be reduced, where precast panels are used. In addition, it is possible to design an exterior formation on the panel having an attractive appearance. In many cases the panel material is concrete, incorporating reinforcement. Typically the thickness of the concrete panelling will be between about one and two inches.
Panels of this thickness require some form of structural reinforcement to provide rigidity. In addition, where such panels are used for exterior load-bearing walls, then they must incorporate some form of structural members.
Typically, such panels will be erected in place to provide a finished exterior, and the interior of the panels will then be covered in and finished at a later stage.
In other applications, the interior of the panels may be prefinished in the factory and insulation may also be installed so that a complete wall system is achieved prior to installation.
Applications for such precast panels are in providing exterior wall systems for commercial and industrial buildings and high rise office buildings and apartments and the like, and also interior wall systems, if desired, with a variety of finishes.
In the majority of cases, such panelling systems are supported on the building structure, and do not normally provide any load bearing capacity, other than resistance to wind loads.
In these cases, the panels must be securely attached to the fabric of building.
The design of such precast panels must, however, be such that it meets all of the foregoing objectives in a satisfactory and efficient manner, and also at a reasonable cost. In most construction projects the actual weight of the material used in construction is of great importance. The weight of the materials affects both the cost of the materials and also the cost of shipping, and imposes limits on the manner in which the materials can be handled at the construction site.
In addition to all of these limitations, however, especially in the construction of high rise buildings, the weight of the construction materials is a critical factor in the design of the entire building.
Where a significant reduction in material weight can be achieved, then it becomes possible to optimize the design of the entire building and reduce construction costs. For all these reasons, therefore, it is desirable that the thickness of the precast panel shall be reduced to a minimum compatible with achieving these objectives.
Accordingly, developments in the design of such precast panelling have been along the lines of reducing the thickness of the panel, and incorporating metal structural studs or channels on the one side of the panel.
In this way, the exterior of the panel presents a finished appearance, and the interior of the panel has a plurality of metal studs or channels partially embedded in its surface.
Using these techniques, it has been found possible to construct precast panels of very considerable size, and of a thickness of between one and two inches.
Reinforcing steel is incorporated in the panels, and the structural steel studs have portions which are embedded in the concrete on one side of reinforcing steel web.
In the past, the steel stud used for this purpose has often been of a simple C-shaped channel, with one edge of the channel simply resting against the reinforcing steel mesh.
This however, is not always a satisfactory method of of attachment. The edge of the channel creates a line of weakness in the panel.
In addition the use of a simple C-shaped channel creates obstructions in the wall. If any electrical services are to be run through the wall, then the openings must be made through the channels.
Another significant problem has been heat transfer through the channels when the panels are used on the exterior of a building. The metal causes patches of cold on the interior walls of the building, resulting in condensation in and on the wall known as "ghosting". The heating load in the building is also increased.
The weight of the metal studs themselves is also a significant factor in the overall weight of the panels. Any reduction in weight that can be achieved, without loss in rigidity, will produce significant benefits.
In some cases it may be desirable to use such panels as floors or roofing, but in the past the studs have been inadequate to support the load.
For all of these reasons therefore it is desirable to provide a precast panel with steel studs which is designed so that the weight of the steel stud is reduced to a minimum, and having its own integral securing means for securing the stud to the precast slab and which incorporates openings along its length which effectively reduces heat transfer through the stud, and which avoids lines of weakness in the slab.